While use has been made of an air bag for protection of an occupant at the time of a side collision, it has been known that the waist of an occupant sitting down first comes into collision with a car's door to be then subjected to an impact, and the chest of the occupant subsequently comes into collision with the car's door.
A conventional air bag device for use as a countermeasure against a side collision used to be structured such that an air bag in its entirety is evenly expanded, however, when trying to sufficiently absorb energy due to the side collision, such a structure as described has turned out inadequate particularly for protection of only the waist, first and foremost, having therefore failed to provide a satisfactory countermeasure against the side collision.
There has been known an air bag device for use as a countermeasure against a side collision (refer to Japanese Patent No. 2933894) developed under the circumstances, incorporating an air bag having two air chambers integral with each other, comprising a lower air bag for protecting the waist of an occupant, on a side of a car body, and an upper air bag for protecting the chest of an occupant, on the side of a car body, wherein a partition wall provided between the upper air bag and the lower air bag has a pressure control valve interposed therebetween, thereby causing the lower air bag to be expanded ahead of the upper air bag.
With the above-described air bag device against the side collision, the air bag expanded in a vertical direction from seat cushion side parts is first inflated up to the height of the waist of the occupant, thereby protecting the waist of the occupant, and continues to be deployed up to the height of the chest of the occupant.
However, if the protection of the head, as well as the waist and chest of the occupant is taken into consideration, when using the air bag against the side collision, while there is, for example, the need for a portion of the air bag, for protecting the waist, reaching a peak pressure before the elapse of 4 ms from expansion of the air bag against the side collision, and thereafter, being quickly reduced in pressure, thereby mitigating a rebound force of the air bag against the side collision, applied to the waist, a portion of the air bag, for protecting the head, needs to keep pressure at a peak value even after the elapse of 12 ms to thereby securely hold the head, so that, in practice, it is necessary not only to differentiate simply in timing for expansion between the respective portions of the air bag against the side collision, but also to differentiate in pressures after the expansion between the respective portions of the air bag, for protecting respective parts of the body of the occupant. Nevertheless, with the conventional air bag device, it is impossible to differentiate in pressure between the upper air bag, and the lower air bag.
Accordingly, with the structure described, there is a problem in that the pressures of the respective portions of the air bag, after the expansion thereof, cannot be optimally adjusted so as to correspond to the respective parts of the body of the occupant.
Accordingly, there has been proposed an air bag device (refer to JP 10-100827A) wherein a partition wall having a communicating part is provided inside a bag-like body of the air bag device, and while the bag-like body is partitioned into first and second chambers, that is, upper and lower ones, there is provided a check valve structured such that an edge of a thin film, at both ends thereof, is fixedly attached to the upper face of the partition wall in such a way as to cover the communicating part, and when gas of the lower chamber flows into the upper chamber, a midpoint part of the check valve is bulged upward in a arch-like state owing to pressure of the gas flowing from the lower chamber into the upper chamber through the communicating part, thereby releasing the check valve so as to allow the gas of the lower chamber to flow into the upper chamber, however, upon addition of outflow pressure of the gas from the upper chamber to the lower chamber, the communicating part is blocked by the midpoint part of the check valve, thereby blocking outflow of the gas from the upper chamber to the lower chamber.
With the air bag device described as above, however, there are the needs for separately preparing the check valve, and attaching it to the partition wall in size large enough to allow the check valve to be attached thereto, causing problems such as an increase in a component count, inability to secure the communicating part in a shape requiring a small gas passage, and so forth.
Now, with the conventional air bag, the upper chamber is formed simply in a bag-like shape, so that it is necessary to cause a large volume of gas to flow into the upper chamber in short time in order to ensure protection of the head of the occupant because the gas from the inflator is diffused throughout the upper chamber when the air bag is expanded. Further, in case that space between the occupant and a door trim, or sidewall is narrow, a gas stream from the portion of the air bag, for protecting the chest (or the waist) of the occupant, to the portion thereof, for protecting the head of the occupant is restricted at the time when the air bag is expanded, so that there is a danger of not only the deployment of the air bag around the head is delayed, but also the portions of the air bag are damaged, or inflicting a direct blow on the occupant, owing to rise in pressure, due to constriction of the gas stream.